Telephone transmitter



Cct. 27, 1925- 1,558,643

A. B. SMITH TELEPHONE TRANSMITTER Filed May v, 1923 M Y f j' Im flhm?BEESEL-f Eh Planea oet/27',

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Y 'm' Ep` TM *N' 'smetta Tov'izllw'hom z'tlmayconoem: p n n Beitvknown'that I; ARTHUR Basenr SMrrn, 'f-a 'citizen of the UnitedvStates of America, and-are'sidentof Evanston, Cook -Colin't'y, '5 andState of Illinois, have invented `'certain new Land nseful4Improvernents in Telephone u Transmitters, of, which the-following' iska specication.4 l i n y y p A My invention relates in general to'telephone transmitters, more in particular tqhtrahsmit'ters iin whichthe microphone velt'e'iient is of the ",igranillar 'Carhol'rL type, fandthe object o f-tho invention isto rovido a microphoneyvhich is welladapted Voropera- ,'15 tion Zonrelatively vlow current values andv,whioh has Vtoojnn;parttively high resistance.

Broadlystated, the desired objectjis'aep coinp'lished byinterposingathin diaphragm ofv-mica orother insulating vmaterial`between. the two electrodes lof the mieiophelie;-A

-The diaphra has a numberzofuopenings through whyio free communicationvis man1- tained` biwen the chambers on Aopposite 'sides thereofeo farasco'ntaetland passage of the granu'lates is' concerned, b't vsflriharedmallenogh, nevertheless, to senslbly l restrict the leectivecross-section of the gralilar ma'ssf In'l additio lthe opemn'gs t are sodisposed as to.a1`pxl7ee1a`blyy lengthen the crrent path between theelectrodes. Thus thelincreased re's'stll is secared` in 3l Y `e precisieImarmeigi'n `which the inten. I tion is carried outwill b descnbedvfullyhereinafter, reference being h ad tO-the ac# oompanying" drawing', inwhich l Flgz 1 1s la cross section throughtl ,well tpe of transmitter.Lnxbodyirlg the inventlon,

while Fig. 2hows the diaphragrin,v hereinifi before Areferred to as banginterposed botv'vgaan the electrodes. ,n Eicept for the microphoneelement, the

5 transmitter myibe '0f any Walkowil fleaigu. l- Aa'illiisnfaai inj the`drawing itoom.A

' almoiltll piece 1; faceplate 2 having anf onelrngfn which tl'l'oYmouth pieee. is

e ,held by screwthreadsj, ,aheyy yflanged rlng 5 3, screed .-"into the:rearwardly extending rimfof the face "plateas shown; a bridge 4,-"which is formed integrally with thefrin'g 8;'.and aiicrophoe cellsupported in the to maman lapin preferablyvof hard rubber, bakelite, .orother sultable insulating material, and on the in- `sido. is oynndrcarin` sha Le for the greater part. of its depth, there eig, however, va'

conical depressionvat thebottom of the cp whlchterminates in acountersnk opening; The stern/9 asses through; this `o ening and a`correspon ing bli'shed hole in brldge 4, and a nut .10, is' employed toclamp. the oup 'to the, bridge. The rear electrode 11 is ofoar;

bonelectropglated dii one l'side and is soldered to the rear end of thestem 9. Its exposed surface isy polished and is iush with the bot`- toinofl the conical depressionjin the op. The. partition 2o, shown mostclearly in' Fig.v 2 is preferably -'of mica, Aperforated,,as shown,andgrests at. the bottom Iof theoylim dricalvpotoof the ciip. To theleft ofthe partition 20` isfabrass ring 19 whose outer edgel isfiushwith the edge of thecx' The.

front electrode 17 is attached vto the ead of 12 in the samelnaner aselectrode 11 is attached -.toi stem, 9, V,and isslightly larger.

diaxneterthanthelatt'er electrode.` I )larhrapfm 21, of micaalso andilsfed forseallngtheend ofthe cup, 1s perforated .in ,the

center to periitfit to be 'slipped in place over fst'ejnfry 12 where itis.A secure 5 and, nut l15; e The diaphfagmel is clamped against thebrass rin" 19 by means of the threaded. cap 18,vcfl1'1'ch also Serves,there-v fore,- lto securely hold the l:said lring and the partition 20.in glace.` -Stem 12 isl agmtby means ofpnut's The' grgnalaarbonis ofoouree intro- Yduced before the op is sealed by lampn'" diaphragm 21 inplace, and should by washer 1o f cient qantity. to nearly, ll 4theCarbon ofthe standard nelne'ss'inay -4 as in ordinary piicrophones, ltheopemngag the partition 20 being much larger than the individual grainsin the standard grade of carbon, so that free circulation 1s maintainedat all times.

In operation, the current cannot pass directly from one electrode to theother, owing to the partition, but must flow outwardly from oneelectrode toward the outside of the mass of carbon in order to passthrough the several openings and reach the other electrode. It will beunderstood therefore that the conducting path through the granulatedcarbon is somewhat longer than it is in the ordinary microphone withoutthe partition, in which the current can pass directly from one electrodeto the other. `It will be noticed also that the partition reduces to aconsiderable extent the effective cross section of the conduct-ing massof carbon; that is, in-

stead of being approximately equal to the actual cross section,theeffective cross section is approximately equal to the sum of the areasof the several openings in the partition, which is a smaller value.

It will be evident from the foregoing that the relative size of theparts, and in particular the size and position of the openings in thepartition, is of great importance in securing the desired results, andthat by suitably varying one or more of the essential dimensions anyresistance desired may be obtained within a considerable range. Thefollowing table gives the principal dimensions in a working transmitterembodying the invention which vgave excellent results:

y Millimeter'. Diameter of 'rear electrode j i 6 Diameter of frontelectrode l 8 Distance between electrodes 2. 1 Numberof openings inpartition; 'i 6 Diameter of vopenings in partition 2. 5 Diameter ofcircle enclosing openings- 11. 2

The transmitter referred to above had a resistance ofapproximately 400ohms workin on a current of .O amperes.

consider to be new and' desire vto have'fprothespace between saidelectrodes, an auxiliary diaphragm parallel to and midway between saidelectrodes, said diaphragm having a centrally located insulated portionequal in size to one of said electrodes, land a plurality of openingsoutside of said insu"- lated portion, said auxiliary diaphragmgreducingthe effective lcross section areafof the comminuted resistance materialand also increasing the length of the currentpath through it.' I

In witness whereoffI 'hereunto subscribe my name this 4th day of May, A.D., 1923.

ARTHUR BESSEY SMITH.

